On Mon, Sep 25, 2006 at 07:11:53PM -0700, Tomas Narvaez wrote:
> Joe:
>
> Thank you for your answer.
> What solution do you propose for high availability?
>
> Regards,
>
> Tomas



It depends on how much money you have. One answer is something like
F5 Network's BigIP/3DNS solution. If you don't have lots of money, it
still depends on how you're configured. Here are some possibilities:

- Two Web servers with different IP addresses. Each one, when booted,
uses some mechanism to try to claim a shared virtual IP address. Use
'wget' or the like to synchronise the content. Use only the virtual
IP address as the Web site's IP address.

- Two synchronised Web servers with different IP addresses. One is
entered into DNS as the Web site's IP address, with a low TTL (if you
think failure likely). An out-of-band mechanism monitors the Web
site's availability. If it goes down, the OOB mechanism changes the
DNS to use the other IP address. And back.

- Two synchronised Web servers with different IP addresses and a shared
virtual IP address, on different networks with different AS numbers.
As long as one remains up, that one's AS advertises the virtual IP
address/network. When it fails, the other AS advertises it.

- Two synchronised Web servers with different IP addresses. Each has a
link to the other, saying: "This is a redundant mirror of this site.
Please bookmark it in case this one goes down."

You trade off money with SOMEBODY's extra effort. ;-)


[NOTE: 3DNS is now called Global Traffic Manager (GTM), but I still need
to look that up.]


--
Joe Yao
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